The present disclosure relates to turbochargers.
A turbocharger is a device with a compressor carried on a common rotor with a turbine, where the turbine drives the compressor to generate compressed air for an engine using the engine's exhaust. Turbochargers often use oil-lubricated fluid film bearings for supporting the turbocharger rotor because fluid film bearings provide high load capacity and durability. Turbochargers for large marine engines are highly refined to operate efficiently at a specified steady-state operation, i.e., the nominal steaming operation, at which the marine vessel will operate continuously for hours, days, weeks, or longer. As the engine operation deviates from the nominal steaming operation, the efficiency of the turbocharger goes down. For example, when the vessel is “slow” steaming, i.e. operating at a slower speed and load than the nominal steaming operation, the loads on the turbocharger rotor are reduced. The turbocharger fluid film bearings, however, are sized to handle in excess of the engine's maximum operating conditions. Thus, at slow steaming, the bearing losses due to the fluid film bearings become a larger proportion of the losses in the turbocharger, impacting the performance of the turbocharger and thus engine efficiency. While reducing the oil flow rate to the fluid film bearings at lower turbocharger rotor loads can reduce the frictional bearing losses, this also can allow the rotor to shift axially, increasing the gap between the compressor and the interior of the housing. This larger gap allows a greater portion of air to bleed by the compressor, thus reducing the turbocharger (i.e., compressor) and engine efficiency.
Like reference symbols in the various drawings indicate like elements.